¢ñ According to the principle of expressing the pressure with the height of the liquid column, a liquid manometer can be used to measure the pressure of the gas or liquid. The simplest manometer is the piezometer.
1.Pressure measuring tube£ºIt is made of a glass tube with a small diameter and fixed on a scale plate to avoid errors caused by surface tension and capillary phenomena. The inner diameter of the glass tube is larger than 5 mm. The upper end of the pressure tube opens to the atmosphere, and the lower end uses a rubber tube. 4Connect with places where pressure is to be measured. When connected, the liquid rises by a certain height h in the piezometer tube. Piezometric tubes have the advantages of simple construction and high accuracy. The disadvantage is that it cannot measure large pressures. Because measuring a large pressure requires a very high piezometric tube, it is not only inconvenient to use, but indoor space is also not allowed. Its measurement range is generally a gauge pressure of less than 0.3 to 0.4 atmospheres, ie a gauge pressure of less than 3 to 4 meters of water.
2.U-tube pressure gauge£ºThe u-tube glass tube is filled with an appropriate amount of mercury, and at the time of application, one end of the U-shaped tube is conceived with the atmosphere. Under the effect of the pressure in the container, the mercury surface in the U-shaped tube produces a height difference. Because u-tubes are often filled with mercury, they are also called mercury piezometers. The tube can also be filled with other liquids, such as water, alcohol, or even oils, when measuring gas pressure. The injected liquid is required not to chemically react with the liquid to be measured, not to mix, and not to volatilize itself.
3. U-tube differential pressure gauge£ºWhen the two ends of the ü-tube manometer are connected to two vessels (or two points of the same vessel) at the same time, the pressure difference between the two vessels (or two points of one vessel) can be measured. The pressure gauge becomes a ü-tube differential pressure gauge. When measuring a large pressure difference, several differential pressure gauges can also be used in tandem.
4. Micro pressure gauge£ºWhen measuring a small pressure (or pressure difference), an inclined micro-pressure gauge is used in order to improve the measurement accuracy. In addition, the smaller the weight of liquid used in the tilted piezometer, the greater the increase in reading. Therefore, liquids with less weight than water, such as alcohol, are commonly used in engineering, which can improve measurement accuracy.
¢òMetal pressure gauge
When the measured pressure is very large, metal pressure gauges are often used. Metal pressure gauges are divided into spring type and thin film type. Among them, spring type pressure gauges are most commonly used.
1. Spring pressure gauge£ºThe main part of the spring-type pressure gauge is a brass-clad tube bent into a guillotine shape. The cross-section of the tube is elliptical, and the closed end is connected with the pointer 2 through a connecting rod 4 or a gear transmission mechanism. The lower end of the tube is connected to the pressure vessel under test. When the pressure is greater than atmospheric pressure fluid into the end tube, the end tube will stretch out, and drive the pointer to turn. When the difference between the pressure of the fluid on the inner and outer walls of the end tube and the elastic force of the tube is balanced, the hands stop rotating. At this time, the gauge pressure of the measured point can be read out by the position of the pointer on the dial 3 . The spring type pressure gauge can measure a great deal of pressure, because its principle of pressure measurement is to use the pressure difference between the inner and outer wall of the tube to make the tube deform, so as long as the resistance to elastic deformation of the tube is large enough, it can measure a great deal of pressure.
2.Film pressure gauge£ºThe main part of the film pressure gauge is a wave-shaped metal film, which is connected to a pointer via a gear or linkage drive. The top of the membrane is open to the atmosphere. When the pressure gauge is placed at the position where the pressure needs to be measured, if the measured pressure is greater or less than atmospheric pressure, the film will bend upwards or downwards and drive the transmission mechanism to rotate the pointer by a certain angle. The measured value can be read on the dial. Point pressure. This instrument can be used as a pressure, vacuum dual-use meter.